PMID:9287004

Citation	Forward, JA, Behrendt, MC, Wyborn, NR, Cross, R and Kelly, DJ (1997) TRAP transporters: a new family of periplasmic solute transport systems encoded by the dctPQM genes of Rhodobacter capsulatus and by homologs in diverse gram-negative bacteria. J. Bacteriol. 179:5482-93
Abstract	The dct locus of Rhodobacter capsulatus encodes a high-affinity transport system for the C4-dicarboxylates malate, succinate, and fumarate. The nucleotide sequence of the region downstream of the previously sequenced dctP gene (encoding a periplasmic C4-dicarboxylate-binding protein) was determined. Two open reading frames (ORFs) of 681 bp (dctQ) and 1,320 bp (dctM) were identified as additional dct genes by insertional mutagenesis and complementation studies. DctQ (24,763 Da) and DctM (46,827 Da) had hydropathic profiles consistent with the presence of 4 and 12 potential transmembrane segments, respectively, and were localized in the cytoplasmic membrane fraction after heterologous expression of the dctQM ORFs in Escherichia coli. DctP, DctQ, and DctM were found to be unrelated to known transport proteins in the ABC (ATP-binding cassette) superfamily but were shown to be homologous with the products of previously unidentified ORFs in a number of gram-negative bacteria, including Bordetella pertussis, E. coli, Salmonella typhimurium, Haemophilus influenzae, and Synechocystis sp. strain PCC6803. An additional ORF (rypA) downstream of dctM encodes a protein with sequence similarity to eukaryotic protein-tyrosine phosphatases, but interposon mutagenesis of this ORF did not result in a Dct- phenotype. Complementation of a Rhizobium meliloti dctABD deletion mutant by heterologous expression of the dctPQM genes from R. capsulatus demonstrated that no additional structural genes were required to form a functional transport system. Transport via the Dct system was vanadate insensitive, and in uncoupler titrations with intact cells, the decrease in the rate of succinate transport correlated closely with the fall in membrane potential but not with the cellular ATP concentration, implying that the proton motive force, rather than ATP hydrolysis, drives uptake. It is concluded that the R. capsulatus Dct system is a new type of periplasmic secondary transporter and that similar, hitherto-unrecognized systems are widespread in gram-negative bacteria. The name TRAP (for tripartite ATP-independent periplasmic) transporters is proposed for this new group.
Links	PubMed PMC179420
Keywords	Adenosine Triphosphate/analysis; Amino Acid Sequence; Amino Acids/analysis; Bacterial Proteins/genetics; Base Sequence; Biological Transport; Carrier Proteins/chemistry; Carrier Proteins/genetics; Carrier Proteins/physiology; Chemotaxis; Cloning, Molecular; Dicarboxylic Acid Transporters; Dicarboxylic Acids/metabolism; Enzyme Inhibitors/pharmacology; Genes, Bacterial/genetics; Gram-Negative Bacteria/genetics; Membrane Potentials; Membrane Proteins/chemistry; Membrane Proteins/genetics; Membrane Proteins/physiology; Membrane Transport Proteins; Molecular Sequence Data; Molecular Weight; Mutagenesis, Insertional; Periplasmic Proteins; Restriction Mapping; Rhodobacter capsulatus/genetics; Rhodobacter capsulatus/metabolism; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Vanadates/pharmacology
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
RHOCA:DCTM		GO:0016021: integral to membrane	ECO:0000314:		C		Fig. 4, Table 2.	complete CACAO 3098
RHOCA:DCTM	part_of	GO:0016021: integral component of membrane	ECO:0000314: direct assay evidence used in manual assertion		C		Seeded From UniProt	complete

References

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